Gemini/GMOS gri pseudo-color image of the central region of PLCK G004.5−19.5. North is up, east is to the left. X-ray surface brightness contours from XMM-Newton are overlaid in white. Spectroscopic cluster members are marked by green circles; only five out of six are visible in the region shown, the sixth member is ~760 kpc to the E-SE of the BCG. Red squares mark the position of the three confirmed multiple images, while we show in red the critical curve for z_s = 1.6. The thin cyan box shows the slit used to get the spectrum of the arc (1″ across); the wide cyan box shows the zoomed-in region in the left panel of Fig. 2. The thick white line in the bottom right corner shows a 30″ scale, corresponding to 188 kpc at z = 0.516.